Refining of lead bullion



Sept. 2, 1930. G, K.l w|| '1AMs 1,774,688

REFINING oF LEAD BULLION Filed March 28, 1929 Jg Z j2me/Wr PatentedSept. `2, 1930 UNITED f sTATEs PATENT OFFICEl REFINING F LEAD BULLIONApplication led March 28, 1929, Serial No. 350,832, and 1n AustraliaApril 11, 1928.

This invention\relates to the refining of" lead lbullion containingother metals such as copper, gold and silver, and refers more especiallyto the refining of bullion working l under similar conditions to what isknown as the Parkes process, that is to say, wherein zinc is added forthe formation of alloys in the form of crusts.

For the purpose of avoiding unnecessary lo repetition in thisspecification the following terms will have the following meaning:

-Alloying metals will means suchmetals as copper or gold or silver whichform alloys with zinc (with or without lead) and which being present inthe initialHbullion, it is desired to remove, both for their own valuesand for the'purposel of providing lead sufficiently free therefrom forcommercial purposes. Crusts will mean and include alloys of the saidalloying metals in the form of crustsl which are formed by the coolingof the bullion with a View to separation from the lead bullion. a5

Residual bullion will mean the bullion remaining after one or more ofthe alloying metals has been separated therefrom in the form of crustsand is relatively low in such alloying metal or metals.

In the refining of lead bullion bythe wellknown IParkes process, it isthe practice to Incorporate a certain amount of zinc with the moltenbullion suicient for the formation of certain" alloys of the alloyingmetals desired to be removed. The bullion is then cooled, whereby thesaid alloys separate from the bullion in the form of crusts, which,owing totheir specific `gravity being lower than that .ofthe liquidbullion, rise to the surface 40`and are then removed, leaving residualbullion relatively low in such alloying metals. The crusts obtained bythe aforesaid Parkes process contain a considerable amount of ventangledlead, the removal of which has '45 Vbeen effectedeitheroysubjecting the saidI crusts to -liquatiomor to'presses. Y',

- p According to a patent in the United States of America which has beengranted to me No. 1,6'87 ,187 ,the treatment for the refining f-llof4 iseffected by incorporating zinc `with the said bullion in sufficientquantity and maintaining such temperatures that molten layers ofconjugate solutions are formed, the upper of which consists of an alloyrich in certain alloyng metal or metals and separating such alloy. Inthe operation of this process it has been applied to effect a continuousrefining of lead bullion', by continuously7 feeding the molten bullioninto a vessel and continuously withdrawing the residual bullion v fromthe bottom thereof, and continuously or intermittently removing thealloy rich in certain alloying metal or metals from the top.

It has hitherto not been possible to effect a continuous refining oflead bullion by the "35 Parkes process. by reason of the fact that it`is necessary to add the requisiJ quantit of zinc, and to heat thebullion'for effecting the solution thereof in the lead, and to thenlcool the mass whereby the alloys are separated out as crusts. Thenature of this operation has hitherto necessitated the carrying out ofthis said Parkes process as an intermittent or batch treatmentoperation. 'l

Now, the object of this invention is to provide a method of operationwhereby the essential conditions and characteristic of the Parkesprocess may be obtained in a c ntinuous operationl as distinct from, onthe one hand the intermittent or batch treatment at 80 presentpractised, and on the other hand from the formation of conjugatesolutions as described in the aforesaid Patent No. 1,687 ,187

I accomplish this object by incorporatin with the bullion an amount ofzinc governe 35 bythe content of alloying metals in\the initial bullionon the one hand and in the residual bullion on the'other hand andsubjecting the `said bullion during its continuous flow to adereasingrange of temperatures, the 11p- ,9u per of which issufficiently high for the solution of thev zinc in thef bullion andbelow the melting point 'of the alloy comprising the crusts to beremoved, Whilst the lower of 'such range is just above the eutectietempera- 95 ture of the residual bullion .desired to be produced,continuously withdrawing the residual bullion and continuously orintermittentp ly removing the crusts accumulating.

.The amount of zinc incorporated with the l bullion is, as stated,governed by the content of the alloying metals in the initial bullionand in the residual bullion, and in determining the amount of zincadditions necessary fregard will be had to the alloys which are formedin the cooler zones and which are redissolved in the bullion in thezones of higher temperature.

The refining operation is carried out in one or more stages theessential feature of the invention being the continuous flow of thebullion through each stage. In practice each stage 1s represented by theflow of the bullion through a kettle or series of kettles or othersuitable vessel in which the Zinc is incorporated with the bullion andthe same subjected to the necessary decreasing range of temperatures. Innormal practice of the Parkes process a stage is generally equivalent towhat is known as a zincing, The invention however may be carried out inother suitable apparatus such as reverberatory furnaces in which thebullion may be subjected to the necessary decreasing range oftemperature.

In the drawings:

Figure 1 is a view in sectional elevational of a series of twoexternally heated kettles adapted for carrying out the invention; and

Figure 2 is a diagrammatic view in elevation illustrating an alternativearrangement of apparatus, and hereinafter is fully de! scribed,

In carrying out this invention the molten bullion is preferably fed intothe top of a suitable kettle (see Fig. l of the drawings) where therequisite quantity of zinc necessary for the later formation of alloysin the form of crusts is incorporated with the bullion the temperaturebeing at the upper part of the said kettle sufliciently high for theincorporation in the bullion of the requisite quantity of zinc, butbelow, the'melting point of the alloys comprising the said crusts,whilst the temperature at the bot-tom of the kettle is maintained justabove the eutectic temperature of the residual bullion, and continuouslywithdrawing the said residual bulh on from the bottom of the kettle, andc-ontinuouslyor intermittently removing the crusts from the top of thesaid kettle.

The shape and dimensions of the kettle in which the operation isconducted may be as shown in Fig. l and are such that the bullion 1npassing therethrough at a certain rate of flow is subject to decreasingtemperatures within the limits mentioned and for this purpose thekettles are so mounted in the brickwork that independent flues E and Fsurround the same so that differential temperatures may be appliedthereto by suit-able means.

In practice the bullion may be pre-heated to any desired temperaturebefore being fed into the top of the kettle such as by means of suitablereverberat-ory furnaces (Figure 2).

The necessary amount of zinc is incorporated with or dissolved in themolten bullion at the top of the kettle either in the f-orm of virginzinc in solid or liquid condition, or in the form of crusts obtainedfrom a previous operation. In practice this zinc is supplemented by theformation of alloys in the form of crusts in the cooler zones which arere-dissolved in the bullion in the hotter zones.

As the bullion passes downward through the kettle into the cooler zones,crusts are formed which rise to the upper part of the kettle, whilst theresidual bullion is continuously withdrawn from the bottom of the kettlein molten condition, either by being pumped or siphoned, or overflowingtherefrom through a suitable spout such as A? which discharges from thebottom and delivers ust below the surface of the bullion. The crustsaccumulating on the surface are removed, either continuously orintermittently by manual or mechanical means as may be desired.

As with the Parkes process this invention is applicable to the treatmentof bullion for the differential separation of alloying metals or for thecollective separation thereof. For example, the operation may beconductedby first obtaining crusts rich in one alloylng metal, such asgold, followed by a subsequent separation of crusts rich in anotheralloy, such as silver, or alternatively crusts may be obtained rich intwo or more alloying metals, such as gold and silver.

Instead of conducting the operation in one kettle, in which the residualbullion is withdrawn just above its eutectic temperature, the operationmay be conducted in two or more kettles in series in which case it wouldonly be necessary that the te-mperature should be maintained just abovethe eutectic temperature of the residual bullion at the outflow from thelast kettle of the series, though it j will be understood that t-heoperation may also be conducted with the temperature at the bottom ofall of the kettles in the series just above the eutectic temperature ofthe residual bullion.

The operation of the Parkes process at present practised is the subjectof a number of different well known `modifications involving mostly thedifferent points at which the additions of Zinc are made, and thisinvention is applicable to any of the said modifications, the essentialpoint being that the cooling of the bullion for the formation of crustsis effected during the continuous passage of the bullion as distinctfrom the intermittent or batch treatment which has hitherto beenincidental to the operation of the said Parkes process. For example theinvention is applicable to the well known modification of theParkesprocess in which two successive zincings are employed, thenecessary zinc for the first zincing being obtained L v from crustsproduced from the second zincing of a previous operation whilst virginzinc is used for the second zincing. l

In applying this invention to this modification of the Parkes process,it is desirable to make use of two kettles as shown in Fig. 1 in series,the outflow from kettle A being delivered into the top of kettle B. Thecrude bullion is continuously fed into the top of kettle A, preferablyhaving been preheated toa temperature suiiicient for the incorporationof the requisite Damount of Zinc in the form of crusts and below themelting point of the orusts which it is desired to remove from the topof this first kettle. This. preheating may be effected in a suitablereverberatory furnace C as shown in Figure 2 The crusts skimmed off fromthe top of kettle B areregularly delivered into the top of kettle A withthe feed of molten crude bullion. The temperature is maintainedindebtain in one the bottom of kettle A at just above the eutectictemperature of the residual bullion being delivered from kettle A and isgoverned by the grade of the metal which it iS desired to deliver tokettle B. The bullion outiiows from A kettle into kettle B, and virginzinc is regularly suppliedto the top of this kettle B in such quantitiesas are necessary for the formation of the alloys with the alloyingmetals contained in the'crude bullion. .The'top of kettle B ismaintained at a temperature suiiiciently high to ensure theincorporation in the bullion of the zinc to be added, but below themelting point of the crusts formed in the said kettle B. In practice thetemperatures at the top of both kettles are approximately the same. The

` bottom of kettle B uis maintained at the temoutflows therefrom.

,perature justl above the eutectic temperature of the residual bullion,which continuously In operation these two kettles` areworking e' inseries in the same manner as obtains with the Parkes process, kettleAbeing directed'v l 'to the formation of crustsof as high a grade Cal ikettle B. lIn this case it will be necessary to as is possible inalloying metals, whilst the kettle B is directed towards the productionof a residual. bullion of as low a content of alloying metals as ispracticable.

ln another \application of this invention operating in two kettlesworking in series, the virgin zinc requisite for the formation of thealloys with the alloying metals contained in the crude bullion may beadded to kettle A as well as the crusts obtained from maintain a highertemperature in the top of kettle A than in the previous example in viewof the higher concentration of zinc and alloying metals, but suchtemperature must be below the melting point of the alloys comprising thecrusts desired to be removed.

The temperature may be maintained at the bottom of kettle A somewhatabove the euteclarger quantity of low tic temperature of the bullionflbwing therefrom Vand may beapproximately the same as the top of kettleB, but the temperature at athe bottom of kettle B is just above theeutectic temperature of the residual bullion.

In practice, however, it is desirable. that the kettle B should bemaintained at a ensuring a more consistent content ofr alloying metal inthe residual bullion discharged from the bottom -of the` said kettle B.It will be obvious that in operating with two kettles inseries with thetemperatures Vof the bottom of kettle Asubstantially the same as the topof kettle B the two kettles are performin the same functions as willkettle of dimensions equalpto the combined depth of the two, the crustsformed in the lower part and cooler zone of the combined kettle beingredissolved in the bullion in its upper part and hotter zone, and thesecrusts will correspond in some degree with those crusts which wouldhave.

been skimmed off from kettle B and regularl fed into'the top of kettleA.

onsequently the invention .may be conducted for the refining of bullionin one kettle, the dimensions of such kettle being such as tonensure'that the decreasing temperatures may be maintained from that at thetop, which is below the melting point of crusts desired to beremoved,and sufficiently high` to ensure the-solution or absorption of the zincadded and the low grade crusts rising to the surface from the coolerzones, to that at the bottom which is just above the eutectictemperature of the residual bullion Y delivered therefrom.

Instead of subjecting the top ofthe kettles or other apparatus in whichthe operation is conducted to external heat for the purpose of obtainingthe necessary temperature, I may preheat the bullion `flowing into thekettle to such a degree as is necessary. vOr alternatively I may preheatthe bullion only to a limited extent with a view to reducing the'external heating of thel top ofthe kettle.

.In conducting-the operation, therefore, it is preferable to preheat thebullion flowing into the kettle A in a small reverberatory furnace C andI have found in practice that external heating of the kettles may beentirevly dispensed with. By interposinga small reverberatory furnaceimmediately before the inflow into `the kettles and causing the bullionto iow therethrough and be preheated'therein to the necessarytemperature to ensure that the bullion has the required degree in thetop ofthe kettles the operatin may beseonducted without any heating ofthe kettles'. -The maintenance of the decreasing- .of two kettles.

temperatures in the kettles to the temperature at the bottom ust abovethe eutectic temperature of the residual bullion may bc obtained byregulating the rate of fiow of the bullion through the kettle or bysubjecting the lower portions of the kettles to cooling means.

The invention therefore lends itself to an exceedingly simplearrangement of plant comprising a series of kettles Gr and H andv smallreverberatory furnaces C and D, the bullion being caused toflowcontinuously through from one reverberatory furnace C to a kettle andthence into another reverberatory furnace D from which it -passes to thenext kettle B in series, the regulation of the temperatures in thekettles being wholly or in part controlled by the temperatures in thesaid reverberatory furnaces C and D.

The followingr example will illustrate one application of this inventionin which preferential removal of crusts relatively rich in gold is firstobtained followed by the removal of crusts relatively rich in silver.

Exemplar-A crude bullion assaying approximately 60-ozs. silver, 100grains gold per ton, and 0.1% copper was continuously preheated in areverberatory furnace and fed into a kettle at the rate of 20 tons perhour, together with an amount of zinc in regular additions equivalent to1 0-lbs. per ton of bullion treated. The preheating of the bullion wassuch as to ensure a temperature at the top of the kettle of 500 C. andthe temperature at the bottom of the kettle at 330 C. The residualbullion was continuously withdrawn from the bottom of the kettle by anoverflow spoilt delivering just below the surface of the metal in thekettle and the crusts accumulating on the surface of the kettle wereskimmed off intermittently.

The residual bullion was found to assay 0.8 grains per ton gold and55-ozs. per ton silver, whilst the crusts removed assayed 8-oZs. per tongold and 200-ozs. perton silver.

The residual bullion flowing from. the above degolding treatment wasthen passed through another reverberatory furnace C for preheating andfed into kettle G of a series The preheating in the reverberatoryfurnace C was such as to'ensure a temperature of ,450 C. at the top ofkettle G and a temperature of 330 C. to- 340 C. at the bottom thereof.The bullion delivered y from thebottoni of kettle G was then passedthrough a furtherreverberatory furnace D and again preheated and fed tothe top of kettle H. The temperature maintained in this lastreverberatory furnace was such as to ensure that the temperature at thetop of kettle H was 450 C. and an amount of zinc equivalent to 16-lbs.per ton of bullion treated lating in the to of kettle H were skimmedfrom time to time and added regularly to the top of kettle G. The crustsaccumulating in the top of kettle G were removed oil' from time to timeand were found to assay 2000 ozs. silver per ton, whilst the residualbullion discharging from the bottom of kettle H assayed 0.15 ozs. silverper ton.

By the application of this invention the refining of bullion may beeffected with a considerable saving in labor as compared with theoperation of the Parkes7 process as hitherto practised. The continuousfiow of the bullion through the kettles or other vessels employeddispenses with the labor incidental to the cooling of the kettles as atpresent practised, and the transfer of bullion from one kettle toanother. The arduous and laborious operation of scraping the kettles asrequired in the present operation of the Parkes process is obviated. Ifthe invention is operated in one kettle of suitable dimensions asdescribed, the skimming of crusts from kettle B is entirely dispensedwith, reducing the labor involved in the skimming by over as comparedwith the Parkes process as at present practiced with two zincings. Inaddition more consistent results can be obtained due to the fact thatthere is less dependence upon manual labor. Again, by dispensing withthe intermittent heating and cooling of the kettles and maintaining eventemperatures upon the kettles during 4the. iow of bullion therethrough.maintenance costs can be reduced due to less wear and tear and breakageof kettles, whilst a considerable saving in fuel can be eeli'cted. Inaddition a reduced plant is necessary for handling a given quantity ofbullion, thereby effecting a considerable saving in capital cost.

I claim:

1.k In th-e continuous refining of lead bullion, incorporating` with thebullion an amount of zinc sufficient for the formation of alloys of oneor more of the alloying metals desired to be removed and a residualbullion relatively low in the said alloying metal or metals andsubjecting the said bullion during lits continuous flow to a decreasingrange of temperatures the upper 'of which is sufliciently higlrfor thesolution or incorporation of the said zinc in the bullion and below themelting point of the alloy comprising the crusts to be removed, whilstthe lower of such range is just above the eutectic temperature of theresidual bullion desired to be produced, continuously withdrawing theresidual bullion and continuously or intermittently removing the crustsaccumulating.

2. In the continuous refining of lead bullion in one or more stages,incorporating with the bullion in each stage of an amount of zinc in theform of virgin zinc and/or I of which is suiciently high for thesolution or incor oration of the said zinc in the bulf'lion but4 elowthe meltinpoint of the alloy comprising the crust to e removed whilstthe lower of such range in the-last stage is just above the eutectictemperature of the residual bullion desired to be produced, continuouslywithdrawing the residual. bullion from the last stage and continuouslyor intermittently removing the crusts accumulating in each stage.

3. In thel continuous refining of lead bullion in one or more stages,incorporating with the bullion in each stage of an amount of zmo in theforml of virgin zinc and/or crusts suicient for the formation ot alloysof one or more of the alloying metals desired tobe removed, and aresidual bullion relatively low in the said alloying metal or metals,and subjecting the bullion in each y stage during its continuous iiowtherethrough to a descreasing range of temperatures, the upper of whichis suiiciently high for the solution or incorporation of the said-zincin the bullion but below the melting point ofthe alloyy comprising thecrust to be removed whilst theJ lower of such ian'ge in the lastE sta-geis just above the eutectic ,temperaturef of the residual bullion desiredto be, pro' duced, continuously withdrawing'the residual bullion `fromthe last stage and continuously or intermittently removing the crustsaccumulating'in each stage, and returning the `crusts accumulating inthe second or sucmetals, and' subjecting the bullionin eac stage duringceeding stages topa preceding sta e.

4. In the continuous refining 0% lead bullion in one or more stages,incorporating with the bullion in each stage of an amount of zinc in theform of virgin zinc and/or crusts sufficient for the formation of alloysof one or more of the alloying metals desired to be removed, and aresidual bullion relatively low inthe said alloying metall or itscontinuous low therethrough to a decreasing range of temperatures theupper of which is suiliciently high for the solution or incorporation ofthe said zinc in the ,bullion but below the melting oint of thealloy.comprising the crust to be removed whilst the lower of 'such'Yrange in the last stage is just abovethe eutectic temperature of theresidual bullion desired to be producedp'continuously withdrawingi P theresidual bullion fromv the'last stage continuously or intermittentlyremovingl the crusts accumulating in each stage, pre eating'fthe bullionprevious to any one stage `to all `form of virgin zinc and/or crusts forkettle or last kettle to be removed, and a residual bullion relativelylow in such alloying metal or metals.

and subjecting the bullion in each stage to a decreasing range oftemperatures, the upper of which is suiiciently high for-the solutionand incorporation of the -said zinc whilst the lower of such rangein thelast sta residual bullion relatively low in the said alloying metal ormetals to be removed, continuously or intermittently removing -thecrusts accumulating in each stage and returning the crusts accumulatingin the second and succeeding stages to a preceding stage, continuouslywithdrawing the said residual bullion, incorporating with the saidresidual bullion in one or more stages of a amount of zinc in the formof virgin zinc the remaining alloyingmetal or metals,

loying metal or metals, and subjecting the bullion in each stage'to adecreasing range of temperatures, the u per of which is sufis just abovethe eutectic temperature o they ficiently high for the solution andincorporation of the said zinc whilst the lower of such range in thelast stage is just above the eutectio temperature of the residualbullion desired to be roduced, withdrawing the said residual bullloncontinuously, and continu,- ously or intermittently removing the crusts,accumulating in each stage and returning the crusts accumulating insucceeding stages to a preceding stage.

6. In the refining of lead bullion,`feeding the .bullion continuouslythrough a kettle or series of kettles, incorporating with the the secondand bullion the necesi-:aryI amount of zinc in the the formation ofalloys of one or more ofPthe alloying metals desired to be removed an aresidual bullion relatively low in the said4 alloying metal or metals,maintaining the bullion in the. top of the said kettles or irst kettleinthe series at a temperature suiiiciently hi h for the solution orincorporation of the said zinc in thel bullion'but below the meltingpoint ofthe alloy comprising the crusts to be produced, maintaining thetemperature o the bullioifat the bottom of the in the series at atemerature just above the eutectictemperature vof the residual bulliondesiredvto be produced, continuously removingthe residual bullion fromthev b last kettle in the series an\d continuously o1( ttom of thekettle er 'e /l intermittently removing the crust accumulating.

7. In 'the refining of lead bullion, feeding the bullion continuouslythrough a kettle together with the necessary amount of zinc for theformation of alloys of one or more of the alloying metals desired to beremoved and a residual bullion relatively l'ow in the said alloyingmetal or metals, maintaining the bullion in the top of the said kettleat a temperature sufficiently high for the solution' or incorporation ofthe said Zinc in the bullion but below the melting point of the alloycomprising the crusts desired to be removed, maintaining the temperatureof the bullion at the bottom of the kettle just above the eutectictemperature of the residual bullion desired to be produced, withdrawingthe residual bullion continuously from the bottom o f the said kettleand continuously or intermittently removing the crusts accumulating onthe top of the said kettle.

8. In the refining of lead bullion, feeding the bullion continuouslythrough a series of two or more kettles together with the necessaryamount of zinc in the form of virgin Zinc and/or crusts for theformation of alloys of one or more of the alloying metals desired to beremoved and a residual bullion relatively low in the said alloying metalor metals, maintaining the bullion at the top of the first kettle in theseries at a temperature sufficiently high for the solution orincorporation of the zine in the bullion but below the melting point ofthe alloy comprising the crusts to be removed from the said kettle,maintaining the temperature of the bullion at the bottom of the lastkettle in the series just above the eutectic temperature of the residualbullion to be produced, feeding the crusts accumulating on the surfaceof the second and succeeding kettles into the top of a preceding kettle,withdrawing the residual bullion continuously from the bottom of thelast kettle in the series and continuously or intermittently removingthe crusts accumulating on the top of the first kettle.

9. In thev refining of lead bullion, feeding the bullion continuouslythrough a kettle or series of kettles, incorporating with the bullionthe necessary amount of zinc in the form of virgin zinc and/or crustsfor tip.: formation of alloys of one or more of the alloying metalsdesired to be' removed and a residual bullion relatively low in the`said alloying metal or metals, preheati'ng the said bullion in areverberatory or other suitable furnace to such a temperature as isnecessary for maintaining the bullion in the top of the kettle or thefirst kettle in the series at a temperature sufficiently high for thesolution at the bottom of the kettle or the last kettle in the series ata temperature just above the eutectic temperature of the residualbullion desired to be produced, withdrawing the residual bullioncontinuously from the bottom of the said kettle or the last kettle inthe series and continuously or intermittently removing the crust-saccumulating on the top of the said kettle.

l0. In the refining of lead bullion, feeding the bullion continuouslythrough a series of two or more-kettles, incorporating with the bullionthe necessary amount of Zinc in the form of virgin zinc and/or crustsfor the formation of alloys of one or more of the alloying metalsdesired to be removed and a residual bullion relatively low in the saidalloying metal or metals, preheating the said bullion in a reverberatoryor other furnace prior to the said bullion being delivered into the topof each of the said kettles in the series whereby the temperature of thebullion is raised therein duringits passage to such a degree as isnecessary for maintaining the bullion in the top of each of the saidkettles at a temperature sufficiently high for the solution orincorporation of the zinc either as virgin zinc or in the form of lowgrade crusts in the bullion, but below the melting point of the alloycomprising the crusts desired to be removed, maintaining the temperatureof the'bullion at the bottom of the last kettle in the series just abovethe eutectic temperature of the residual bullion desired to be produced.feeding the crusts accumulating on the surface of the second orsueceeding kettles into the top of a preceding kettle, withdrawing theresidual bullion continuously from the bottom ofthe last kettle in theseries and continuously or intermittently removing the crustsaecumulating'on the top of the said kettle.

ll. In the refining of lead bullion, feeding the bullion continuouslythrough two or more series of kettles, incorporatingwith the bullionduring its passage through the first series the necessary amount of zinein the form of virgin zinc and/or crusts for the preferential formationof alloys of one or more of the alloyi'ag metals and a residual bullionrelatively low in such alloying metal or metals maintaining the bullionat the top of the first kettle of the first series at a temperaturesufficiently high for the solution or incorporation of the said Zinc inthe bullion, but below the melting point of t-he alloy comprising thecrusts to be removed, maintaining the temperature of the bullion at thebottom of the said last kettle of the first series just below theeutectic temperature of the residual bullion relatively low in the saidalloying metal or metals to be preferentially removed, continuouslydischarging the residual bullion into the succeeding seriesincorporating with the bullion during its passage through the saidsucceeding series the necessary amount of zinc in the form of vi'rginzinc and/or crusts for theV formation of alloys of the remainingalloying metal or metals desired to be removed and obtaining a residualbullion desired to be produced and relatively low in such alloyingmetals, withdrawing the said residual bullion continuously from thebottom of the last kettle and continuously or intermittently removingthe crusts accumulat ing in the said succeeding series of kettles'relatively high in the said remaining alloying metal or metals. l2. Inthe rening of lead bullion, feeding the bullion into a reverberatory orother suitable furnace for preheating it to the required temperature anddischarging the said preheated bullionv into the top of the first of twoseries of kettles, togetherA with the necessary amount of zinc for theformationof alloys in the form of crusts relatively rich in one or moreof the alloying metals (such as gold) and obtaining a residual bullionrelatively rlow in the said alloying metal or metals continuouslypassing the said bullion through the first series of kettles anddischarging the same continuously from the bottom of the last kettle .inthe rst series at a temperature just above the eutectic temperature ofthe residual bullion relatively low in the said second series,withdrawing the residual bullion continuously from the bottom of thesecond kettle in the second series relatively low in the said alloyingmetal or metals and continuously or intermittently removing the crustsaccumulating in the top of the first kettle of the second seriesrelatively high ir the said alloying metal -or metals.

In witness whereof -I hereunto af'x my signature.

GEORGE KENNETH WILLIAMS.

alloying metal or metals, continuously or intermittently removing thecrusts relatively rich in such alloying metal or metals from the top ofthe first kettle, in the first series, feeding the bullion to a'reverberatory or other suitable furnace in which it is preheated-to thedesired temperature and then feeding the same continuously through thesecond series of kettles, feeding anamount of Zinc into the' firstkettle of the second series sufficient for the formation of alloys inthe form of crusts l relatively high in the remaining alloying same Intothe second kettle of the second se# ries, feeding the crustsaccumulating on the surface of --the second kettle of the second seriesinto the top ofthe first kettle of the

